SOLUTION

The silicon-controlled rectifier usually referred to as an SCR, is one of the families of semiconductors that includes transistors and diodes. Another name for the SCR is thyristor. It is similar to a diode with an additional terminal that is used to turn it on. Once turned on, the SCR will remain on as long as current flows through it. If the current falls to zero, the SCR behaves like an open switch. This device is much larger in size than a transistor or a MOSFET and it is designed to operate at higher voltages and currents, typically 1,000 V or higher, and 100 A or higher.

SCRs are mainly used where high currents and voltages are involved and are often used to control alternating currents, where the change of sign of the current causes the device to automatically switch off. Like a diode, an SCR conducts only in one direction. A similar 5-layer device, called a triac,  conducts current in both directions.

Characteristics of SCR

• SCR are semiconductor devices that can operate only in the switching mode.
• The SCR is a current operated device, a small Gate current controls a larger Anode current.
• The SCR Conducts current only when they are forward biased and triggering current is applied to the Gate.
• The SCR acts as a rectifying diode once it is triggered “ON”.
• Anode current must be greater than the holding current to maintain conduction.
• Blocking current flow when reverse biased, no matter if Gate current is applied or not
• Once turned on, the SCR will remain on as long as current flows through it.